My 4Runner has been making a weird sound that I haven’t been able to diagnose, and I’m hoping folks here might have some ideas. Video with sound recording linked below, I cannot figure out how to embed a YouTube video, sorry! It’s the ccchhh-ccchhh-ccchhh sort of sound, and seems to be more noticeable later in the attached recording.

- 1999 4Runner V6 SR5 4WD Manual, 290k miles.
- The sound seems to be coming from between the engine and the fire-wall, maybe in the vicinity of the Idle Air Control Valve or the Fuel Pressure Regulator, maybe lower, maybe outside the engine, hopefully not inside the engine. (I have chronic eustachian tube dysfunction so admittedly can’t locate the sound precisely.)
- It’s been giving Check Engine Light code P0420.
- I replaced the vacuum hoses around the charcoal canister with silicone hoses (from HPS Performance) over a year ago. Smog tech did not like them when I tried to smog it a few months ago so I swapped to Napa rubber hoses to get it through smog. The CEL came on during the drive home from smog. I swapped back to silicone and clamped all the hoses to see if this would solve the issue, then turned the CEL off, but it came back on right away.
- Fuel pump was replaced in mid-April by a local Toyota specialty shop (“preventative maintenance,” it was the original fuel pump). I noticed this sound after bringing the 4Runner home from the shop. The sound does seem to be getting louder each time I drive it, so it’s possible it was making the noise before it went in for the fuel pump, but I’m not sure.
- It doesn’t seem to make the sound when it first starts (cold start), but it does start making the noise once it’s warmed up.
- The sound may or may not be unrelated to the CEL code and/or the fuel pump replacement, I don’t know.

I love this old 4Runner, my parents bought it new when I was a toddler, and even though it’s starting to have more and more issues I still want to keep it forever.

I’m hoping someone here might have encountered this issue and/or have some advice? Thank you in advance!!

4R Diagnostics - YouTube

Sounds like an exhaust leak to me. That could contribute to the P0420 also.

Could be bad manifold gaskets or bad exhaust manifold to crossover pipe gaskets.

The bolt could be corroded tight and a challenge to remove.

Much luck to you

Great to know, thank you! That definitely sounds like it is probably the issue! I’ll take a look and see if it might be something I can handle myself (though, yes, those bolts probably are pretty corroded, especially given that the ones between the cat and the muffler look really bad), otherwise I’ll schedule it in at the shop, but either way knowing what it most likely is the source of that odd sound is a huge help. Thanks!